navigator.onLine
and the related events can be useful when you want to update your UI to indicate that you’re offline and, for instance, only show content that exists in a cache.
But I’d avoid writing service worker logic that relies on checking navigator.onLine
. Instead, attempt to make a fetch()
unconditionally, and if it fails, provide a backup response. This will ensure that your web app behaves as expected regardless of whether the fetch()
fails due to being offline, due to lie-fi, or due to your web server experiencing issues.
// Other fetch handler code...
if (event.request.mode === 'navigate') {
return event.respondWith(
fetch(event.request).catch(() => caches.match(OFFLINE_URL))
);
}
// Other fetch handler code...